UBI will come - soon
The principle is very easy to understand. Assume I have a factory that can make electric toasters for £5 each, staffed entirely by robots, with distribution by driverless lorries. I have no staff. If every other factory works the same way, then none of us have any customers for our cheap toasters, as no-one has any income. Result - unsold toaster mountain.
UBI is just a simple and cheap mechanism to ensure that all in a society benefit from the advances of technology. As a society we've steadily mechanised, and as a result productivity has increased, so that we won the fight for a 40-hour week. No-one should now be doing 12 hour days, six days a week. This is just taking it to the next logical stage.
A key feature of UBI is that it is very basic. Enough for food, clothing, shelter and not much more. If people want more, then they work - but not 40 hours a week. For every pound they earn they will pay some tax, but they will also keep some of it. Goodbye benefits trap. For people who cannot work they will continue to receive some benefits. Pensioners will receive some pension (which they have paid for and earned).
It can and will work. But the vested interests fighting it will be as hard to overcome as Big Oil, Big Tobacco and Big Pharma.